LCD projection lens

ABSTRACT

A projection lens for use with a pixelized panel (LCD) is provided. The lens has two positive lens units with an aperture stop between them. The optical powers of each of the units are such that f1 is substantially shorter than f2, where f1 and f2 are the focal lengths of the first lens unit and the second lens unit, respectively, the first lens unit being on the system&#39;s long conjugate side and the second lens unit being on the short conjugate side. The ratio of f1 to f2 is preferably less than about 0.75.

CROSS REFERENCE TO RELATED PROVISIONAL APPLICATION

This application claims the benefit under 35 USC §119(e) of U.S. Provisional Application No. 60/016,447 filed Apr. 29, 1996 the content of which in its entirety is hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to projection lenses and, in particular, to projection lenses which can be used, inter alia, to form an image of an object composed of pixels, such as, a liquid crystal display (LCD).

BACKGROUND OF THE INVENTION

Projection lens systems (also referred to herein as "projection systems") are used to form an image of an object on a viewing screen. The basic structure of such a system is shown in FIG. 7, wherein 10 is a light source (e.g., a tungsten-halogen lamp), 12 is illumination optics which forms an image of the light source (hereinafter referred to as the "output" of the illumination system), 14 is the object which is to be projected (e.g., a matrix of on and off pixels of a LCD panel), and 13 is a projection lens, composed of multiple lens elements, which forms an enlarged image of object 14 on viewing screen 16.

Projection lens systems in which the object is a LCD or other pixelized panel are used in a variety of applications, including data display systems. Such projection lens systems preferably employ a single projection lens which forms an image of either a single panel having, for example, red, green, and blue pixels, or three individual panels, one for each color. For ease of reference, the following discussion will be in terms of a projection lens system that employs a single LCD panel, it being understood that the invention can also be used in systems which employ multiple panels and/or other types of pixelization.

SUMMARY OF THE INVENTION

The projection lenses of the invention comprise two positive lens units with an aperture stop between them. The optical powers of each of the units are such that f1 is substantially shorter than f2, where f1 and f2 are the focal lengths of the first lens unit and the second lens unit, respectively, the first lens unit being on the system's long conjugate side and the second lens unit being on the short conjugate side. In particular, the ratio of f1 to f2 is less than about 0.75. (See Table 7 and note that when the second unit includes a field lens, e.g., a Fresnel field lens, the value of f2 is calculated without the field lens.) In contrast, for a classical double gauss form, f1 is about the same as f2, or longer than f2.

The projection lenses of the invention are capable of covering a wide field of view. They have a back focal length approximately equal to the focal length of the lens. Each of the first and second lens units has at least one aspherical surface.

The first lens unit on the long conjugate side of the stop may consist of a single positive element. However, to obtain a better correction of residual astigmatism and chromatic aberrations, this unit may include a leading negative element closely followed by a positive component which may be a color correcting doublet. As illustrated in Tables 1-5, the spacing between the leading negative element and the positive component is at most about 5% of the focal length of the first lens unit.

The second lens unit behind the aperture stop includes a color correcting doublet and a single positive element with at least one aspherical surface. Most of the correction of spherical aberration is obtained in the first lens unit, while off-axis aberrations including coma and distortion, as well as chromatic aberrations, are corrected predominantly in the second lens unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-6 are schematic side views of projection lenses constructed in accordance with the invention.

FIG. 7 is a schematic diagram showing an overall projection lens system in which the projection lens of the present invention can be used.

The foregoing drawings, which are incorporated in and constitute part of the specification, illustrate the preferred embodiments of the invention, and together with the description, serve to explain the principles of the invention. It is to be understood, of course, that both the drawings and the description are explanatory only and are not restrictive of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 to 6 illustrate various projection lenses constructed in accordance with the invention. Corresponding prescriptions and optical properties appear in Tables 1 to 6, respectively. The correspondence between the lens units discussed above and the various elements and surfaces of the lenses of Tables 1-6 is set forth in Table 7.

HOYA or SCHOTT designations are used for the glasses employed in the lens systems. Equivalent glasses made by other manufacturers can be used in the practice of the invention. Industry acceptable materials are used for the styrene and acrylic elements.

The aspheric coefficients set forth in the tables are for use in the following equation: ##EQU1## where z is the surface sag at a distance y from the optical axis of the system, c is the curvature of the lens at the optical axis, and k is a conic constant.

The designation "a" associated with various surfaces in the tables represents an aspheric surface, i.e., a surface for which at least one of D, E, F, G, H, or I in the above equation is not zero. The designation "c" represents a conic surface for which the k value in the above equation is not zero. The designation "f" represents a Fresnel lens surface (the Fresnel lens is identified by the designation "FL" in FIGS. 1 and 3). All dimensions given in the tables are in millimeters. The tables are constructed on the assumption that light travels from left to right in the figures. In actual practice, the viewing screen will be on the left and the LCD panel will be on the right, and light will travel from right to left.

Although specific embodiments of the invention have been described and illustrated, it is to be understood that a variety of modifications which do not depart from the scope and spirit of the invention will be evident to persons of ordinary skill in the art from the foregoing disclosure.

                                      TABLE 1                                      __________________________________________________________________________     Lens Data                                                                      Surf.                             Clear Aperture                               No.  Type   Radius Thickness Glass                                                                               Diameter                                     __________________________________________________________________________      1   a      -1770.1750                                                                            8.00000   ACRYLIC                                                                             84.11                                         2   a      72.5195                                                                               10.00000       71.77                                         3          63.3660                                                                               25.00000  SK18 68.98                                         4          -63.3660                                                                              4.00000   KF6  65.89                                         5          762.9749                                                                              9.16228        60.48                                         6          Aperture stop                                                                         35.18800       57.72                                         7          -38.4192                                                                              5.00000   SF14 63.38                                         8          -81.9407                                                                              1.00000        80.13                                         9   a      -77.4031                                                                              18.00000  ACRYLIC                                                                             83.60                                        10   a      -57.0000                                                                              Space 1        93.65                                        11   c      -927.4539                                                                             29.50000  ACRYLIC                                                                             119.77                                       12   a      -79.0000                                                                              Space 2        124.99                                       13   cf     185.6000                                                                              4.00000   ACRYLIC                                                                             237.06                                       14          ∞                                                                               Image distance 236.86                                       __________________________________________________________________________     Symbol Description                                                                              a -- Polynomial asphere                                                        c -- Conic section                                                             f -- Fresnel                                                  __________________________________________________________________________     Conics                                                                                    Surface                                                                        Number                                                                             Constant                                                        __________________________________________________________________________                11  -7.1739E+01                                                                13  -1.7000E+00                                                     __________________________________________________________________________     Even Polynomial Aspheres                                                       Surf.                                                                          No.                                                                               D      E      F      G      H      I                                        __________________________________________________________________________      1 -7.0051E-08                                                                           -6.3254E-12                                                                           -2.9530E-14                                                                            7.5364E-19                                                                            9.4792E-21                                                                           -3.0013E-24                               2  7.7762E-08                                                                            1.2679E-11                                                                            1.0260E-13                                                                           -3.2966E-17                                                                           -1.6803E-21                                                                            1.6991E-23                               9  4.1171E-07                                                                            2.1244E-10                                                                            1.0122E-14                                                                            4.0619E-18                                                                            4.4932E-21                                                                           -1.0666E-24                              10  2.4362E-07                                                                            1.2454E-10                                                                            1.2955E-14                                                                            1.0067E-17                                                                            1.8340E-21                                                                            3.0151E-24                              12  1.3759E-07                                                                            5.0414E-11                                                                           -2.7910E-15                                                                            1.1423E-18                                                                            3.9343E-23                                                                           -3.3950E-27                              __________________________________________________________________________     Variable Spaces                                                                Zoom       Space 1                                                                            Space 2      Focal                                                                              Image                                          Pos.       T(10)                                                                              T(12)        Shift                                                                              Distance                                       __________________________________________________________________________     1          1.500                                                                              182.411      -1.425                                                                             10.021                                         2          0.500                                                                              190.200      -1.000                                                                             10.015                                         3          2.000                                                                              175.350      -1.800                                                                             10.013                                         __________________________________________________________________________     First-Order Data                                                                              Zoom Position                                                                  1           2    3                                              __________________________________________________________________________     f/number       3.50        3.50 3.50                                           Magnification  -0.0645     -0.1000                                                                             -0.0322                                        Object Height  -1830.8     -1180.0                                                                             -3660.0                                        Object Distance                                                                               -3048.7     -1998.8                                                                             -6010.2                                        Effective Focal Length                                                                        198.28      202.52                                                                              194.61                                         Image Distance 10.021      10.015                                                                              10.013                                         Overall Length 3391.4      2348.3                                                                              6346.5                                         Forward Vertex Distance                                                                       342.78      349.56                                                                              336.21                                         Barrel Length  332.76      339.55                                                                              326.20                                         Stop Surface Number                                                                           6           6    6                                              Distance to Stop                                                                              0.00        0.00 0.00                                           Stop Diameter  55.244      56.621                                                                              54.042                                         Entrance Pupil Distance                                                                       40.838      40.838                                                                              40.838                                         Exit Pupil Distance                                                                           -2564.2     -2859.8                                                                             -2270.8                                        __________________________________________________________________________     First Order Properties of Elements                                             Element                                                                               Surface                                                                 Number Numbers Power  f'     lpp    l'pp                                       __________________________________________________________________________     1       1  2   -0.70980E-02                                                                          -140.88                                                                               5.1374 -0.21047                                   2       3  4    0.18681E-01                                                                          53.532 8.2520 -8.2520                                    3       4  5   -0.88988E-02                                                                          -112.38                                                                               0.20149                                                                               -2.4261                                    4       7  8   -0.10095E-01                                                                          -99.059                                                                               -2.6268                                                                               -5.6025                                    5       9 10    0.29494E-02                                                                          339.06 35.393 26.063                                     6      11 12    0.57837E-02                                                                          172.90 21.342 1.8179                                     7      13 14    0.26604E-02                                                                          375.88 -0.51716E-08                                                                          -2.6778                                    __________________________________________________________________________     First-Order Properties of Doublets                                             Element                                                                               Surface                                                                 Numbers                                                                               Numbers Power  f'     lpp    l'pp                                       __________________________________________________________________________     2 3    3 5      0.11187E-01                                                                          89.389 1.5277 -16.542                                    __________________________________________________________________________     First Order Properties of Groups                                               Group  Surface                                                                 Number Numbers Power  f'     lpp    l'pp                                       __________________________________________________________________________     1       1 10   -0.26248E-03                                                                          -3809.7                                                                               495.35 349.41                                     2      11 12    0.57837E-02                                                                          172.90 21.342 1.8179                                     3      13 14    0.26604E-02                                                                          375.88 -0.51716E-08                                                                          -2.6778                                    __________________________________________________________________________     First Order Properties of the Lens                                             Zoom Position                                                                  Number         Power  f'     lpp    l'pp                                       __________________________________________________________________________     1               0.50433E-02                                                                          198.28 223.78 -199.63                                    2               0.49377E-02                                                                          202.52 228.97 -211.76                                    3               0.51385E-02                                                                          194.61 218.81 -189.07                                    __________________________________________________________________________

                                      TABLE 2                                      __________________________________________________________________________     Lens Data                                                                      Surf.                             Clear Aperture                               No.  Type   Radius Thickness Glass                                                                               Diameter                                     __________________________________________________________________________      1   a      -3501.6551                                                                            8.00000   ACRYLIC                                                                             83.97                                         2   a      73.8047                                                                               10.00000       72.07                                         3          63.9262                                                                               25.00000  SK18 69.86                                         4          -63.9262                                                                              4.00000   KF6  67.04                                         5          570.3825                                                                              2.53228        60.39                                         6          ∞                                                                               41.97092       59.72                                         7          -39.0852                                                                              5.00000   SF14 64.45                                         8          -83.4350                                                                              1.00000        80.90                                         9   a      -77.4031                                                                              18.00000  ACRYLIC                                                                             83.88                                        10   a      -57.0000                                                                              0.50000        94.26                                        11   c      -927.4539                                                                             30.50000  ACRYLIC                                                                             119.04                                       12   a      -79.0000                                                                              194.22819      124.60                                       __________________________________________________________________________     Symbol Description                                                                              a -- Polynomial asphere                                                        c -- Conic section                                                             Focal Shift = -1.97869                                        __________________________________________________________________________     Conics                                                                                    Surface                                                                        Number                                                                             Constant                                                        __________________________________________________________________________                11  -7.5322E+01                                                     __________________________________________________________________________     Even Polynomial Aspheres                                                       Surf.                                                                          No.                                                                               D      E      F      G      H      I                                        __________________________________________________________________________      1 -8.1680E-08                                                                           -9.0415E-12                                                                           -2.8846E-14                                                                            9.7292E-19                                                                            9.4877E-21                                                                           -2.8507E-24                               2  6.1549E-08                                                                            5.4266E-12                                                                            9.8518E-14                                                                           -3.4835E-17                                                                           -1.5392E-21                                                                            1.7744E-23                               9  3.8615E-07                                                                            1.8759E-10                                                                            1.0984E-14                                                                            7.6281E-18                                                                            5.6048E-21                                                                           -1.6720E-24                              10  2.7112E-07                                                                            1.4686E-10                                                                            1.7530E-14                                                                            1.0200E-17                                                                            1.4695E-21                                                                            2.8348E-24                              12  1.1260E-07                                                                            4.4374E-11                                                                           -2.9777E-15                                                                            1.1981E-18                                                                            4.3134E-23                                                                           -6.5187E-27                              __________________________________________________________________________     First-Order Data                                                               f/number    3.50       Overall Length                                                                            3505.33                                      Magnification                                                                              -0.0645    Forward Vertex Distance                                                                   340.731                                      Object Height                                                                              -1830.8    Barrel Length                                                                             146.503                                      Object Distance                                                                            -3164.60   Entrance Pupil Distance                                                                   40.9073                                      Effective Focal Length                                                                     198.998    Exit Pupil Distance                                                                       -145.903                                     Image Distance                                                                             194.228    Stop Diameter                                                                             57.224                                       Stop Surface Number                                                                        6          Distance to Stop                                                                          6.43                                         __________________________________________________________________________     First Order Properties of Elements                                             Element                                                                               Surface                                                                 Number Numbers Power  f'     lpp    l'pp                                       __________________________________________________________________________     1       1  2   -0.68364E-02                                                                          -146.28                                                                               5.2411 -0.11047                                   2       3  4    0.18530E-01                                                                          53.965 8.2460 -8.2460                                    3       4  5   -0.90617E-02                                                                          -110.35                                                                               0.26468                                                                               -2.3616                                    4       7  8   -0.99405E-02                                                                          -100.60                                                                               -2.6199                                                                               -5.5926                                    5       9 10    0.29494E-02                                                                          339.06 35.393 26.063                                     6      11 12    0.57859E-02                                                                          172.83 22.057 1.8788                                     __________________________________________________________________________     First Order Properties of Doublet                                              Element                                                                               Surface                                                                 Numbers                                                                               Numbers Power  f'     lpp    l'pp                                       __________________________________________________________________________     2 3    3 5      0.10898E-01                                                                          91.762 1.1692 -6.833                                     __________________________________________________________________________     First Order Properties of the Lens                                                            Power  f'     lpp    l'pp                                       __________________________________________________________________________                    0.50252E-02                                                                           199.00 119.64 -15.627                                    __________________________________________________________________________     FIRST ORDER DATA, SURF 1 TO 5                                                  K           PP1           PP2  f'                                              __________________________________________________________________________     0.490176E-02                                                                               30.3186       -1.10148                                                                            204.00                                          __________________________________________________________________________     FIRST ORDER DATA, SURF 7 TO 12                                                 K           PP1           PP2  f'                                              __________________________________________________________________________     0.232360E-02                                                                               147.569       172.803                                                                             430.37                                          __________________________________________________________________________

                                      TABLE 3                                      __________________________________________________________________________     Lens Data                                                                      Surf.                             Clear Aperture                               No.  Type   Radius Thickness Glass                                                                               Diameter                                     __________________________________________________________________________     1    a      -148.4666                                                                             6.00000   ACRYLIC                                                                             51.92                                        2    a      54.4747                                                                               0.50000        45.04                                        3           40.0292                                                                               15.00000  SK18 45.07                                        4           -130.3723                                                                             6.26676        42.15                                        5           Aperture stop                                                                         21.40605       34.58                                        6           -23.1527                                                                              3.00000   SF13 39.96                                        7           -64.2034                                                                              1.50000        54.39                                        8           -54.0449                                                                              16.67610  ACRYLIC                                                                             54.69                                        9    a      -35.8273                                                                              0.50000        63.68                                        10   a      -3465.3279                                                                            24.66862  ACRYLIC                                                                             93.09                                        11   a      -54.7193                                                                              121.94030      95.74                                        12   cf     120.0000                                                                              4.00000   ACRYLIC                                                                             166.79                                       13          ∞                                                                               9.99997        166.48                                       __________________________________________________________________________     Symbol Description                                                                              a -- Polynomial asphere                                                        c -- Conic section                                                             f -- Fresnel                                                                   Focal Shift = -1.94463                                        __________________________________________________________________________     Conics                                                                                    Surface                                                                        Number                                                                             Constant                                                        __________________________________________________________________________                12  -2.0085E+00                                                     __________________________________________________________________________     Even Polynomial Aspheres                                                       Surf.                                                                          No.                                                                               D      E      F      G      H      I                                        __________________________________________________________________________      1 -1.0532E-06                                                                           -1.0364E-09                                                                            1.3079E-12                                                                           -2.2637E-15                                                                            4.0754E-18                                                                           -2.4681E-21                               2 -1.0077E-06                                                                            1.3853E-10                                                                           -5.4208E-12                                                                            1.3555E-14                                                                           -3.2354E-18                                                                           -5.1055E-21                               9 -7.2513E-07                                                                            1.8571E-09                                                                           -2.8477E-12                                                                            1.3532E-1S                                                                            6.7032E-19                                                                           -5.6155E-22                              10 -2.1332E-07                                                                            2.4887E-11                                                                            3.2458E-14                                                                            8.2905E-18                                                                            2.9285E-22                                                                           -1.2661E-25                              11  5.7413E-07                                                                            4.5720E-11                                                                            4.8259E-14                                                                            2.5315E-17                                                                           -1.5472E-20                                                                            9.1310E-24                              __________________________________________________________________________     First-Order Data                                                               f/number    3.50       Overall Length                                                                            1401.46                                      Magnification                                                                              -0.1083    Forward Vertex Distance                                                                   231.458                                      Object Height                                                                              -762.00    Barrel Length                                                                             221.458                                      Object Distance                                                                            -1170.00   Entrance Pupil Distance                                                                   20.3913                                      Effective Focal Length                                                                     129.271    Exit Pupil Distance                                                                       5729.90                                      Image Distance                                                                             9.99997    Stop Diameter                                                                             34.576                                       Stop Surface Number                                                                        5          Distance to Stop                                                                          0.00                                         __________________________________________________________________________     First Order Properties of Elements                                             Element                                                                               Surface                                                                 Number Numbers Power  f'     lpp    l'pp                                       __________________________________________________________________________     1       1  2   -0.12511E-01                                                                          -79.928                                                                               2.9100 -1.0677                                    2       3  4    0.20219E-01                                                                          49.458 2.2234 -7.2414                                    3       6  7   -0.19987E-01                                                                          -50.032                                                                               -0.99970                                                                              -2.7722                                    4       8  9    0.60514E-02                                                                          165.25 25.425 16.855                                     5      10 11    0.89025E-02                                                                          112.33 16.739 0.26432                                    6      12 13    0.41148E-02                                                                          243.03 -0.82019E-08                                                                          -2.6778                                    __________________________________________________________________________     First Order Properties of the Lens                                                            Power  f'     lpp    l'pp                                       __________________________________________________________________________                     0.77357E-02                                                                          129.27 152.58 -131.33                                    __________________________________________________________________________

                                      TABLE 4                                      __________________________________________________________________________     Lens Data                                                                      Surf.                             Clear Aperture                               No.  Type   Radius Thickness Glass                                                                               Diameter                                     __________________________________________________________________________      1   a      -143.9480                                                                             6.00000   ACRYLIC                                                                             52.57                                         2   a      54.0933                                                                               0.50000        46.45                                         3          39.9766                                                                               15.00000  SK18 47.01                                         4          -138.3967                                                                             6.26676        44.55                                         5          ∞                                                                               23.26477       37.09                                         6          -23.3945                                                                              3.00000   SF13 41.34                                         7          -57.7517                                                                              1.50000        55.58                                         8          -50.6040                                                                              16.57162  ACRYLIC                                                                             56.00                                         9   a      -36.2946                                                                              0.50000        64.89                                        10   a      -2367.8999                                                                            24.39444  ACRYLIC                                                                             92.92                                        11   a      -54.6713                                                                              134.17166      95.59                                        __________________________________________________________________________     Symbol Description                                                                              a -- Polynomial asphere                                                        Focal Shift = -1.24114                                        __________________________________________________________________________     Even Polynomial Aspheres                                                       Surf.                                                                          No.                                                                               D      E      F      G      H      I                                        __________________________________________________________________________      1 -7.8786E-07                                                                           -7.4301E-10                                                                            1.2284E-12                                                                           -2.6558E-15                                                                            3.7917E-18                                                                           -1.8308E-21                               2 -4.9688E-07                                                                            6.2284E-10                                                                           -5.5378E-12                                                                            1.2528E-14                                                                           -4.7256E-18                                                                           -2.2320E-21                               9 -6.7035E-07                                                                            1.6035E-09                                                                           -2.8384E-12                                                                            1.4275E-15                                                                            6.5802E-19                                                                           -6.1437E-22                              10 -2.4379E-07                                                                            2.3325E-11                                                                            3.2535E-14                                                                            8.2976E-18                                                                            2.0542E-22                                                                           -2.1158E-25                              11  6.0221E-07                                                                            5.9205E-11                                                                            4.6922E-14                                                                            2.3851E-17                                                                           -1.6076E-20                                                                            8.9490E-24                              __________________________________________________________________________     First-Order Data                                                               f/number    3.50       Overall Length                                                                            1473.17                                      Magnification                                                                              -0.1083    Forward Vertex Distance                                                                   231.169                                      Object Height                                                                              -762.00    Barrel Length                                                                             96.9976                                      Object Distance                                                                            -1242.00   Entrance Pupil Distance                                                                   20.8429                                      Effective Focal Length                                                                     129.736    Exit Pupil Distance                                                                       -136.607                                     Iinage Distance                                                                            134.172    Stop Diameter                                                                             36.897                                       Stop Surface Number                                                                        5          Distance to Stop                                                                          0.45                                         __________________________________________________________________________     First Order Properties of Elements                                             Element                                                                               Surface                                                                 Number Numbers Power  f'     lpp    l'pp                                       __________________________________________________________________________     1       1  2   -0.12684E-01                                                                          -78.838                                                                               2.8906 -1.0862                                    2       3  4    0.19996E-01                                                                          50.010 2.1178 -7.3318                                    3       6  7   -0.18289E-01                                                                          -54.677                                                                               -1.2146                                                                               -2.9983                                    4       8  9    0.53197E-02                                                                          187.98 28.371 20.349                                     5      10 11    0.88539E-02                                                                          112.94 16.659 0.38462                                    __________________________________________________________________________     First Order Properties of the Lens                                                            Power  f'     lpp    l'pp                                       __________________________________________________________________________                    0.77080E-02                                                                           129.74 85.332 -8.3775                                    __________________________________________________________________________     FIRST ORDER DATA, SURF 1 TO 4                                                  K           PP1           PP2  f'                                              __________________________________________________________________________     0.825105E-02                                                                               11.8672       -1.63760                                                                            121.20                                          __________________________________________________________________________     FIRST ORDER DATA, SURF 6 TO 11                                                 K           PP1           PP2  f'                                              __________________________________________________________________________     0.412919E-02                                                                               105.968       138.422                                                                             242.18                                          __________________________________________________________________________

                                      TABLE 5                                      __________________________________________________________________________     Lens Data                                                                      Surf.                             Clear Aperture                               No.  Type   Radius Thickness Glass                                                                               Diameter                                     __________________________________________________________________________      1   a      -215.0838                                                                             6.00000   ACRYLIC                                                                             50.10                                         2   a      51.3941                                                                               0.50000        44.84                                         3          39.5202                                                                               15.00000  SK18 45.08                                         4          -204.0199                                                                             6.26676        41.86                                         5          ∞                                                                               24.70386       37.34                                         6          -23.5819                                                                              3.00000   SF13 42.80                                         7          -54.9838                                                                              17.48359  SK5  58.11                                         8          -38.5513                                                                              0.50000        68.16                                         9   a      -442.7462                                                                             22.96924  ACRYLIC                                                                             93.18                                        10   a      -54.6936                                                                              133.38308      95.54                                        __________________________________________________________________________     Symbol Description                                                                              a -- Polynomial asphere                                                        Focal Shift = -1.06757                                        __________________________________________________________________________     Even Polynomial Aspheres                                                       Surf.                                                                          No.                                                                               D      E      F      G      H      I                                        __________________________________________________________________________      1 -6.2558E-07                                                                           -6.6007E-10                                                                            1.3377E-12                                                                           -2.7764E-15                                                                            3.6207E-18                                                                           -1.7047E-21                               2 -4.7729E-07                                                                            2.8390E-10                                                                           -5.2520E-12                                                                            1.3608E-14                                                                           -6.5024E-18                                                                           -3.3618E-21                               9 -4.6643E-08                                                                            3.6819E-11                                                                            2.8968E-14                                                                            8.8163E-18                                                                            1.7148E-21                                                                            2.3288E-25                              10  5.3589E-07                                                                            1.0862E-10                                                                            4.8657E-14                                                                            2.7503E-17                                                                           -1.4201E-20                                                                            9.3743E-24                              __________________________________________________________________________     First-Order Data                                                               f/number    3.50       Overall Length                                                                            1471.80                                      Magnification                                                                              -0.1083    Forward Vertex Distance                                                                   229.807                                      Object Reight                                                                              -762.00    Barrel Length                                                                             96.4234                                      Object Distance                                                                            -1241.99   Entrance Pupil Distance                                                                   19.6498                                      Effective Focal Length                                                                     129.598    Exit Pupil Distance                                                                       -136.742                                     Image Distance                                                                             133.383    Stop Diameter                                                                             37.137                                       Stop Surface Number                                                                        5          Distance to Stop                                                                          -0.86                                        __________________________________________________________________________     First Order Properties of Elements                                             Element                                                                               Surface                                                                 Number Numbers Power  f'     lpp    l'pp                                       __________________________________________________________________________     1      1  2    -0.11992E-01                                                                          -83.389                                                                               3.2180 -0.76895                                   2      3  4     0.18904E-01                                                                          52.899 1.5196 -7.8449                                    3      6  7    -0.17354E-10                                                                          -57.623                                                                               -1.3444                                                                               -3.1347                                    4      7  8     0.63978E-02                                                                          156.30 26.344 18.471                                     5      9 10     0.80676E-02                                                                          123.95 17.207 2.1256                                     __________________________________________________________________________     First Order Properties of Doublets                                             Element                                                                               Surface                                                                 Numbers                                                                               Numbers Power  f'     lpp    l'pp                                       __________________________________________________________________________     3 4    6 8     -0.76835E-02                                                                          -130.15                                                                               -25.890                                                                               -48.110                                    __________________________________________________________________________     First Order Properties of the Lens                                                            Power  f'     lpp    l'pp                                       __________________________________________________________________________                    0.77162E-02                                                                           129.60 83.934 -9.1868                                    __________________________________________________________________________     FIRST ORDER DATA, SURF 1 TO 4                                                  K                    PP1  PP2                                                  __________________________________________________________________________     0.754490E-02         10.2057                                                                             -3.41220                                             __________________________________________________________________________     FIRST ORDER DATA, SURF 6 TO 10                                                 K                    PP1  PP2                                                  __________________________________________________________________________     0.446394E-02         93.0606                                                                             115.413                                              __________________________________________________________________________

                                      TABLE 6                                      __________________________________________________________________________     Lens Data                                                                      Surf.                              Clear Aperture                              No.  Type   Radius Thickness Glass Diameter                                    __________________________________________________________________________     1    a      94.4760                                                                               15.00000  STYRENE                                                                              42.78                                       2    a      -528.9612                                                                             0.50000         37.32                                       3           ∞                                                                               21.29889        36.84                                       4           -27.7690                                                                              3.00000   STYRENE                                                                              40.46                                       5    a      -407.8987                                                                             4.00000         53.21                                       6           -74.3345                                                                              12.15783  BK7   53.55                                       7           -42.4453                                                                              0.50000         61.02                                       8    a      164.4718                                                                              26.97190  ACRYLIC                                                                              92.86                                       9    a      -62.3055                                                                              135.01787       95.37                                       __________________________________________________________________________     Symbol Description                                                                              a -- Polynomial asphere                                                        Focal Shift = -0.74200                                        __________________________________________________________________________     Even Polynomial Aspheres                                                       Surf.                                                                          No.                                                                               D      E      F      G      H      I                                        __________________________________________________________________________     1  -2.1948E-07                                                                           -3.1161E-09                                                                            7.4142E-12                                                                           -1.0377E-14                                                                           -2.2299E-17                                                                            3.2858E-20                              2  -1.5111E-06                                                                           -5.1899E-09                                                                           -8.6485E-12                                                                            2.3336E-14                                                                            2.8430E-17                                                                           -1.0133E-19                              5  -3.9131E-07                                                                           -6.8333E-10                                                                            5.5582E-13                                                                            6.5433E-16                                                                            1.3386E-20                                                                           -7.1347E-22                              8  -2.9686E-07                                                                           -3.7064E-12                                                                            9.5859E-15                                                                            4.9355E-18                                                                            1.5459E-21                                                                            5.8285E-25                              9   5.6173E-07                                                                            1.1183E-10                                                                            1.3209E-14                                                                            1.5832E-17                                                                           -1.7718E-20                                                                            7.9237E-24                              __________________________________________________________________________     First-Order Data                                                               f/number    3.50       Overall Length                                                                            1460.42                                      Magnification                                                                              -0.1083    Forward Vertex Digtance                                                                   218.446                                      Object Height                                                                              -762.00    Barrel Length                                                                             83.4286                                      Object Distance                                                                            -1241.97   Entrance Pupil Distance                                                                   14.3855                                      Effective Focal Length                                                                     128.370    Exit Pupil Distance                                                                       -110.515                                     Image Distance                                                                             135.018    Stop Diameter                                                                             35.707                                       Stop Surface Number                                                                        3          Distance to Stop                                                                          3.27                                         __________________________________________________________________________     First Order Properties of Elements                                             Element                                                                               Surface                                                                 Number Numbers Power  f'     lpp    l'pp                                       __________________________________________________________________________     1      1 2      0.73555E-02                                                                          135.95 1.4381 -8.0518                                    2      4 5     -0.19908E-01                                                                          -50.232                                                                               -0.13781                                                                              -2.0243                                    3      6 7      0.59254E-02                                                                          168.76 16.511 9.4276                                     4      8 9      0.10498E-01                                                                          95.259 13.631 -5.1638                                    __________________________________________________________________________     First Order Properties of the Lens                                                            Power  f'     lpp    l'pp                                       __________________________________________________________________________                    0.77900E-02                                                                           128.37 71.383 -7.9999                                    __________________________________________________________________________     FIRST ORDER DATA, SURF 4 TO 9                                                  K                    PP1  PP2                                                  __________________________________________________________________________     0.444232E-02         92.8040                                                                             107.813                                              __________________________________________________________________________

                  TABLE 7                                                          ______________________________________                                                Unit 1   Unit 2                                                         Ex. No.                                                                               Surf. Nos.                                                                              Surf. Nos.                                                                              f1    f2    f     f1/f2                               ______________________________________                                         1      1 to 5   7 to 12  199.16                                                                               448.33*                                                                              198.99*                                                                              0.444                               2      1 to 5   7 to 12  204.00                                                                               430.37                                                                               199.00                                                                               0.474                               3      1 to 4   6 to 11  115.38                                                                               257.84*                                                                              129.60*                                                                              0.447                               4      1 to 4   6 to 11  121.20                                                                               242.18                                                                               129.74                                                                               0.500                               5      1 to 4   6 to 10  132.56                                                                               224.02                                                                               129.60                                                                               0.592                               6      1 to 2   4 to 9   135.95                                                                               225.11                                                                               128.37                                                                               0.604                               ______________________________________                                          *Value calculated without the Fresnel lens since the Fresnel lens is           primarily a field lens which serves to couple the lens' entrance pupil to      the exit pupil of the illumination system. As such, the Fresnel lens has       minimal effect on the overall focal length of the lens, but a large effec      on the value of f2, which effect is not representative of the actual           functioning of the f2 unit.                                               

What is claimed is:
 1. A projection lens for forming an image of an object, said lens having an aperture stop and consisting in order from its image end to its object end of:(a) a first lens unit having a positive optical power and a focal length f1; (b) a second lens unit having a positive optical power and a focal length f2;wherein the aperture stop is located between the first and second lens units, f1 is shorter than f2, and the lens has a back focal length approximately equal to the lens' focal length.
 2. The projection lens of claim 1 wherein the second lens unit has a negative lens element at its image end.
 3. The projection lens of claim 1 wherein said lens has a focal length f and f1/f is less than or equal to 1.1.
 4. The projection lens of claim 3, 1, or 2 wherein the ratio of f1 to f2 is less than about 0.75.
 5. The projection lens of claim 3, 1 or 2 wherein each of the first and second lens units has at least one aspherical surface.
 6. The projection lens of claim 3, 1 or 2 wherein the first lens unit consists of a single positive lens element.
 7. The projection lens of claim 3, 1 or 2 wherein the first lens unit comprises in order from its image end:(a) a negative lens element; and (b) a positive lens subunit.
 8. The projection lens of claim 7 wherein the positive lens subunit is spaced from the negative lens element by a distance which is less than or equal to 5% of f1.
 9. The projection lens of claim 8 wherein the second lens unit comprises a color correcting doublet and a positive lens element which has at least one aspherical surface.
 10. The projection lens of claim 7 wherein the second lens unit comprises a color correcting doublet and a positive lens element which has at least one aspherical surface.
 11. The projection lens of claim 7 wherein the positive lens subunit is a color correcting doublet.
 12. The projection lens of claim 11 wherein the second lens unit comprises a color correcting doublet and a positive lens element which has at least one aspherical surface.
 13. The projection lens of claim 3, 1, or 2 wherein the second lens unit comprises a color correcting doublet and a positive lens element which has at least one aspherical surface.
 14. A projection lens system for forming an image of an object, said system comprising:(a) an illumination system comprising a light source and illumination optics which forms an image of the light source; (b) a pixelized panel which comprises the object; and (c) the projection lens of claim 3, 1, or
 2. 15. The projection lens system of claim 14 further comprising a field lens between the pixelized panel and the projection lens.
 16. The projection lens of claim 2 wherein the lens has a focal length f and f1/f is less than or equal to 1.1. 